Some electronic cameras generate color image data by using an image sensor on which color filters in three colors (R, G, B: red, green, blue) are arranged on predetermined positions (such as in a Bayer array).
In this kind of electronic cameras, each of the pixels of the image sensor outputs color information on a single color component alone. Thus, processes for enhancing the image by providing each pixel with color information corresponding to three color components have been practiced.
Among such processes heretofore practiced is a color interpolation process. Specifically, similarity of each pixel in conjunction with the directions to its adjacent pixels is judged, and interpolation values (values that are equivalent to the color information corresponding to color components not contained in respective pixels) are obtained in accordance with the judgement result.
Moreover, Japanese Unexamined Patent Application Publication No. 2000-78597 (U.S. Pat. No. 6,075,889) discloses technology for performing a process of generating a luminance value and a “chrominance value” for each pixel. That is, enhancement of an image is achieved through the processing in which each pixel is provided with the color components of a colorimetric system different from the colorimetric system that was adopted in the image at the time of generation by the image sensor. Here, the luminance values of the respective pixels are generated, being classified into five similarity directions, which are a horizontal direction, vertical direction, flat, diagonal direction 1, and diagonal direction 2.
According to the technology disclosed in the foregoing publication, however, luminance values are basically generated from color information corresponding to two color components, as is evident from how the luminance values of pixels containing color information corresponding to the red component or color information corresponding to the blue component are generated. Consequently, the luminance values generated at the respective pixels become uneven in RGB ratios pixel by pixel, and the RGB ratios of the generated luminance values vary greatly each time the target pixel of the luminance value generation moves on. Thus, there has been a high possibility that false structures not existing in the photographic object (false structures attributable to the Bayer array) appear as structures varying pixel by pixel over chromatic areas and flat areas in particular.
Moreover, according to the technology disclosed in the foregoing publication, the generated luminance values are corrected with correction values which vary depending on the directions of similarity at the respective pixels. Such correction values are extracted from “blurred luminance values” whose high frequency components pertaining to structural factors are all broken. Hence, the high frequency components have been corrected only insufficiently, with the results lacking in high frequency components.
Furthermore, according to the technology disclosed in the foregoing publication, since chrominance is generated with reference to luminance values that are generated from color information over a wide range, local high frequency components tend to disappear and color artifacts easily occur.
That is, it has been impossible to expect image enhancement with high precision from the technology disclosed in the foregoing publication.